During the manufacture and assembly of electronic display devices such as for example cathode ray (CRT) assemblies for complex monitors and television sets, precise mechanical, magnetic and electronic adjustments are required to ensure the electronic display devices provide optimum reproduction image quality. These adjustments include, but are not limited to, focus, purity of color, convergence of beams, color uniformity, geometry and luminance.
Purity of color or beam landing errors are a result of misalignment between the electron beams generated by the electronic display device and the phosphor elements thereof. Ideally, the electron beams are coincident with the phosphor elements so that the phosphor elements emit light at maximum intensity. Unfortunately, it is common during manufacture of the electronic display devices for the electron beams generated by the electronic display devices to be misaligned with the phosphor elements on which the electron beams are to impinge. Therefore, during the testing and alignment of electronic display devices, it is necessary to measure beam landing errors so that measures can be taken to correct them.
Test and alignment systems to test and adjust electronic display devices are known, such as for example those described in U.S. patent applications Ser. Nos. 08/750,522 and 08/670,694, assigned to the assignee of the present invention. These test and alignment systems include at least one wobulator generating magnetic fields to deflect electron beams within electronic display devices to allow beam landing errors to be measured. Many techniques have been considered to measure electron beam landing errors using a wobulator.
For example, U.S. Pat. No. 4,814,858 to Mochizuki et al., discloses a method for measuring beam landing errors using symmetrical, constant amplitude wobulation to move electron beams within the electronic display device. As the electron beams are moved, highly magnified images of illuminated and non-illuminated phosphor elements are taken and approximated with ellipses and circles in order to calculate beam landing errors. Unfortunately, this method is only suitable for measuring electron beam landing errors in electronic display devices having dot-type phosphor patterns and requires microscopic images of the illuminated phosphor elements to be examined.
In the article entitled "Design and Implementation of an Automatic Adjustment System for Integrated Tube Components" authored by S. R. Kim et al. and published in Mechatronics 1994, a method similar to the above-described technique is disclosed. However, this technique is adapted for electronic display devices in the form of color picture tubes including striped phosphor patterns and a shadow mask having elongate vertical openings with rounded rods therein. In this method, the detailed shapes of the top and bottom of greatly magnified illuminated phosphor elements are analyzed and conclusions of electron beam landing errors are made based on the asymmetricity of the analyzed shapes. Unfortunately, this method is also only suitable for a specific class of color picture tubes and requires microscopic images of the illuminated phosphor elements to be examined. Also, it is necessary to average several microscopic images due to the lack of uniformity of features of the illuminated phosphor elements.
U.S. Pat. No. 4,688,079 to Fendly discloses a method wherein a wobulator is used to deflect electron beams to adjacent different color phosphor elements. Knowing the periodicity and dimension of the phosphor element pattern and the current required to push the electron beams to adjacent phosphor elements and by measuring the current required to center the electron beams on their own phosphor elements, an equation can be determined to calculate electron beam landing errors based on the intensity of the illuminated phosphor elements. Unfortunately, this method requires large magnetic fields to deflect the electron beams to adjacent phosphor elements. Also, this method uses as reference the phosphor element pitch which often varies over the dimension of the electronic display device. Also, due to lack of uniformity between phosphor element features, averaging is required. Accordingly, an improved method of measuring beam landing errors within an electronic display device is desired.
It is therefore an object of the present invention to provide a novel method system for measuring beam landing errors within an electronic display device.